Running vehicles on ethanol rather than petrol can increase ground-level ozone pollution, according to a study of fuel use in São Paulo, Brazil.Ozone (O3) is a major urban pollutant that can cause severe respiratory problems. It can form when sunlight triggers chemical reactions involving hydrocarbons and nitrogen oxides (NOx) emitted by vehicles.

Ethanol has been promoted as a ‘green’ fuel because its combustion tends to produce lower emissions of carbon dioxide, hydrocarbons and NOx than petrol. But the impact on air quality of a wholesale transition from petrol to ethanol has been difficult to assess, with different atmospheric chemistry models predicting a variety of consequences.

Alberto Salvo, an economist at the National University of Singapore, and Franz Geiger, a physical chemist at Northwestern University in Evanston, Illinois, have now answered the question with hard data. Their study, published today in Nature Geoscience, unpacks what happened when the motorists of São Paulo — the largest city in the Southern Hemisphere — suddenly changed their fuel habits.

Sugar high
In 2011, about 40% of the city’s 6 million light vehicles — mostly cars — were able to burn pure ethanol or a petrol-ethanol blend, and both fuels were widely available. Consumers in São Paulo thus had more choice over their fuel than almost anywhere else in the world, says Salvo. Between 2009 and 2011, the price of ethanol rose and fell in response to fluctuations in the global prices of sugar, which is used to produce ethanol via fermentation. But the government-controlled gasoline price remained steady. This led to a huge shift in fuel consumption — wholesalers’ figures suggest that gasoline’s share of total transport fuel rose from 42% to 68%. “Our study is the only one where you have a large switch over a relatively short timescale,” says Salvo.

São Paulo also has an extensive network of air-monitoring stations that record the atmospheric consequences of its notorious traffic congestion. Salvo and Geiger collated these air-quality measurements and used other data sets — detailing meteorological and traffic conditions, for example — to weed out other factors that would have affected air quality over that period. Overall, they report, the rise in gasoline consumption caused an average drop of 15 micrograms per cubic meter (15 μgm–3) in ground-level ozone concentration, down from a weekday average of 68 μgm–3.

But air-quality campaigners should not start advocating for petrol instead of ethanol quite yet. Increased petrol burning clearly raised levels of NOx, which also poses direct health concerns, and it probably boosted the amount of particulate matter in the air, something the study did not look at. And because every city has its own unique air chemistry, a similar fuel switch might produce very different results in London or Los Angeles. Nevertheless, says Salvo, the findings illustrate that “ethanol is not a panacea”.

Opportunity NOx
So how could burning more petrol, which puts more of the ingredients for ozone formation into the air, actually reduce São Paulo’s ozone levels?

As nitrogen dioxide becomes more abundant in the air, it increasingly combines with hydroxyl radicals to form nitric acid. This removal of hydroxyl radicals shuts down the reaction that forms ozone. “It’s a really strong quenching effect,” says Sasha Madronich, an atmospheric chemist at the US National Center for Atmospheric Research in Boulder, Colorado, who wrote an accompanying News and Views article on the São Paulo study. At high NOx levels, this quenching begins to outweigh ozone synthesis, and ozone levels drop.

Theoretical models have predicted that such an ‘NOx-inhibited’ situation could arise in cities with relatively high NOx levels, but “it’s never been observed, because there’s no place to observe it”, says Geiger.

The researchers say that their method of combining disparate data sets to tease out the effects of fuel changes could now be used in other cities. Geiger acknowledges that São Paulo is “the best-case scenario in terms of data availability”, but hopes to apply the same method to Chicago, Illinois, which might enable his team to predict the impact of a major shift to vehicles powered by electricity or natural gas, for example.

And by uncovering the real-world impact of fuel changes in São Paulo, the researchers have provided a useful test bed for air-pollution models, adds Madronich. “If a model cannot reproduce these results,” he says, “that’s a problem for the model.”
***

By Mark Peplow and Nature magazine | Scientific American |

This article is reproduced with permission from the magazine Nature. The article was first published on April 28, 2014.

Friday May 2, 2014, 6:37 am
> Running vehicles on ethanol rather than petrol can increase ground-level ozone pollution
= interesting. That "agro-fuls" are (overwhelmingly) an IDIOCY (see down below), I was well aware of; but this little detail had hitherto escaped my attention.

Btw., Natural gas vehicles --like some of the (public) busses in VIE; and often describesd as 'cleaner'-- also increase ground-level O3/NOx pollution. I don't need any study to tell me, for my nose tells me without a doubt.

Friday May 2, 2014, 12:00 pm
WOW this is shocking research.awareness, though I should not be surprised, since we were FORCED to switch to the more COSTLY PROCESSED crap (whose PROCESSING ALONE POISONS US) under the guise of it being necessary TO SAVE THE ENVIRONMENT FROM TOXIC POLLUTION!

Friday May 2, 2014, 12:04 pm
YES THEY FORCED THIS COSTLY PROCEDURE TO MAKE $, MORE % PROFITS. ACTUALLY COSTS MORE GAS/MILE & IT POLLUTES THE ENVIRONMENT even MORE considering the PROCESSING, now ADDITIONALLY here we find the more toxic effects it actually has on the entire ecosystem, including the atmospheric which it purportedly professed to alleviate.

It was all about money, all along. ALSO CONSIDER SUBSIDIES PAID BY GOVERNMENT, WHICH COMES FROM PEOPLES TAX $, THAT WAS USED TO PUSH THIS AGENDA, ALSO TO GROW MONSANTO STAR CORN, WHICH IS TOXIC TO LIFE, THE ENVIRONMENT, & WAS PUSHED FOR ANIMAL FEED & PROCESSING ~~~~ETHANOL~~~!!!

Friday May 2, 2014, 12:30 pm
My grandson-in-law is a master mechanic and he told me soon after Ethanol started being used that he and other mechanics realized that Ethanol Destroys Auto Engines. Beware of using ethanol. It did nothing good but only raised our food prices across the board and all over the country. It was such a stupid idea to burn our food source in automobiles.

Friday May 2, 2014, 12:54 pm
GMO CORN (Star corn) originally approved in the 90's SUBSIDIZED BY THE GOVERNMENT ( = your TAX DOLLAERS) to provide resources for ETHANOL, later to allegedly REDUCE FOOD COSTS, also approved for livestock feed only, NOW GMO CORN IS APPROVED IN YOUR MARKET, in almost everything you buy. IT IS NOT SAFE!

SO WE GOT FORCED TO USE ETHANOL WHICH POLLUTES THE ENVIRONMENT IN PROCESSING, DOES NOT OFFER BETTER MILEAGE, wrecks engines, & messes with the global climate in an incidious but MAJOR way... ALSO we are now forced to buy those subsidized GMO food crops that cause disease, kill the bees (well harm all flora, fauna, including you & me!)

Friday May 2, 2014, 12:58 pm
It was/is all being done in the name of "what's good for US" but as more are becoming aware we must be very wary of what agenda's being promoted. NONE of the subsidized advancements in energy/mileage & food distribution have had a positive outcome, & ALL have had deleterious effects.

Friday May 2, 2014, 2:23 pm
Ethanol is not and was not ever a "green" fuel. Forests are destroyed to plant sugar cane, with a lot of pesticides. Then before harvesting the huge crops are burned in huge fires. And then the processing - which smells horribly - pollutes all the rivers were the left overs are thrown. Not speaking of the slave labor used in the harvesting.
Botton line is: there is no green fuel or energy whatsoever. The only answer is that we must re-evaluate our needs of fuel/energy and decide we need less.

Ethanol is green only in the sense that it makes a lot of money for both the investors and those "gambling" on the commodities market. It does not make gasoline cleaner nor is it good for the environment.

Friday May 2, 2014, 4:45 pm
We need to get as much onto solar as fast as we can, supplemented by wind. Everyone here knows that, so all we need to do is get it past the Koch Brothers. Yeah, right, good luck with that.

Just when you think the Koch brothers and like minded have deep fingers in the elections and all hope is lost, enter Tom Steyer with a billionaire check book and plans to spend against the republican agenda, a guy that is wealthy and still "gets it" that people are under paid and hungry, that climate change is not guess work but scientific research. He has also pledged to give away at least half of his money in his life time. Amazing!

Friday May 2, 2014, 4:55 pm
It is increasingly unlikely that human beings will take a big step outside of their ideological boxes and actually look at science and do what must be done to survive climate change. We must get off fossil fuels now. Every alternative has significant environmental risks and/or impacts. We are not going to get through this unscathed; and we are going to be disappointed when so many of our best efforts have unintended consequences. But it's either do what we can or accept extinction.

Friday May 2, 2014, 4:57 pm
Ethanol is a big cheat, not only because it maintains our dependence on the internal combustion engine, but also because ethanol production robs food out of the mouths of those who need those crops the most.

Friday May 2, 2014, 5:08 pm
Of course, it takes no brains to not care about the thousands of species that will be negatively impacted by the development of a thousand square miles of pristine desert. Who knows? There might even be enough power to light 30% of Los Angeles on a clear day. Solar is an excellent form of energy, but all forms of energy have environmental impacts...and none of it amounts to real progress, if human civilization is rapidly increasing its consumption of fossil fuels even as it increases alternative energy development.